Programmable timing devices, such as frequency synthesizers, must have a basic set of configuration parameters at each power-on of the timing device in order to generate the required timing device output signals for a processor board. Typically, at a power-on of the processor board, typically referred to as a “power-on-reset”, the frequency synthesizer receives a configuration from the processor board through a logical interface of the programmable timing device, such as an Inter-Integrated (I2C) interface or a system management bus (SMB) interface. The configuration for the frequency synthesizer may alternatively be received from a nonvolatile memory device such as a Read Only Memory (ROM). During the power-up of the processor board, the configuration for the frequency synthesizer is loaded into the phase locked loop (PLL circuit of the frequency synthesizer and is used to control the behavior of the frequency synthesizer, including setting one or more frequencies of the output signals of the PLL circuit.
Changing the default values of PLL circuit effects the behavior of the frequency synthesizer. Typically, the default values are modified or programmed through the logical interface of the frequency synthesizer. However, when the processor board and the frequency synthesizer are being initialized, the processor is unable to modify the configuration to effect the associated behavior of the PLL circuit until the initialization of the processor board and the frequency synthesizer is complete, and the logical interface is accessible. There are times when it is advantageous to be able to modify the behavior of the frequency synthesizer from the default setting as part of the board re-initialization or to modify the behavior of the frequency synthesizer without utilizing the logical interface.
Accordingly, what is needed in the art is a system and method for modifying the behavior of a frequency synthesizer that does not rely on a logical interface to provide the modified default values for configuring the frequency synthesizer.